Japan resumed the death penalty in 1993 after a 40-month pause. Thursday's executions left 104 inmates still on Japan's death row.

Human rights groups condemned the action.

"The abolition of the death penalty is now a global trend, with 135 countries legally or effectively terminating it, but Japan goes against the trend, and moreover, it has accelerated executions," Amnesty International Japan said.

Makoto Miyazaki, chairman of the Japan Federation of Bar Associations, urged the government to suspend the death penalty to allow for a public debate, Kyodo reported.